Group transmissions, having one multi-speed main transmission and one splitter group front-mounted thereon by drive technology, the same as a range change group rear-mounted on the main transmission by drive technology, have been known for a long time and are preferably used in industrial vehicles. The ratio jumps of the main transmission are halved by one splitter group designed generally with two speeds, having in about half of a middle ratio jump, between two consecutive ratio stages of the main transmission, a corresponding ratio jump and the number of gears of the group transmission altogether available is doubled. By a range change group, usually of two speeds with one ratio spanning over the whole ratio jump of the main transmission by about one middle ratio jump, between two consecutive ratio stages of the main transmission, the spread of the whole transmission is approximately doubled and the number of the total gears of the group transmission altogether available is again doubled. Relative to a three-speed main transmission (with three forward speeds and one reverse speed), this results in one 12-gear group transmission with altogether twelve forward gears and a maximum of four reverse gears and in relation to a four-speed main transmission, having four forward gear stages and one reverse gear stage, a 16-gear group transmission results and has a total of sixteen forward gears and a maximum of four reverse gears. Such a group transmission has, in comparison with a single transmission with a similar number of gears and similar gear gradation and spread, clearly more compact dimensions and lighter weight. But since many gear shifts in a group transmission require the change of ratio stages in several parts of the transmission and thus the sequence is relatively complicated, most known group transmissions are constructed such that they are either partly automated or fully automatedly shiftable.
A general view of the Applicant's automated group transmissions has been published in a periodical ATZ September 2004, pages 772-783. To the series of products of automated shift transmission, designated as AS-Tronic Family, belong the transmissions of the AS-Tronic middle line of products built for medium heavy industrial vehicles and the transmissions of the AS-Tronic line of products provided for heavy industrial vehicles, each designed as group transmission with one multi-speed, that is, main transmissions provided with three or four forward stages, one two-speed, splitter group front-mounted on the main transmission and one two-speed, range change group rear-mounted on the main transmission. The main transmission is constructed in countershaft design provided with unsynchronized dog clutches having, in the case of the AS-Tronic line of products, two countershafts for reasons of weight and space optimation. In both lines of products, the main transmission is optionally available in a direct gear design (iHG—min=1) or in a fast gear design (iHG—min<1). The splitter group is designed as a countershaft transmission with two shiftable, input constants for the main transmission. The range change group is designed as a two-speed, planetary transmission with one shiftable direct connection (iGP=1) and one alternatively shiftable high ratio (iGP>>1).
A group transmission, having one multi-speed, main transmission in countershaft design, one splitter group front-mounted thereon with two shiftable input constants of the main transmission and one range change group in planetary design rear-mounted on the main transmission is, moreover, known from WO 1999/00612 A1. This known group transmission can be optionally designed as a direct transmission by equipment with a different gear wheel pair forming an input constant of the main transmission or as a fast gear transmission. One alternative to this, of a group transmission with one two-speed, main transmission in countershaft design (with two forward gear stages and one reverse gear stage), one three-speed, splitter group front-mounted thereon and one range change group in planetary design rear-mounted on the main transmission, has been described in EP 0 769 641 B1.
In the group transmissions of the AS-Tronic line of products and of the AS-Tronic middle line of products have been built with synchronized shift clutches of the splitter group and of the range change group, combined in a common shift set, whereas the main transmission was designed to be shifted with a dog clutch, that is, shiftable by way of unsynchronized dog clutches. But since the concerned synchronized shift clutches, due to a complicated construction, are relatively more expensive, need a relatively large amount of space and, as a result of wear, the duration of the whole group transmission is limited for future designs of such group transmissions. It could be provided that, together with the main transmission, the range change group is also a dog shifted designed.
Due to the unsynchronized design of the range change group in such a group transmission, a special shifting sequence is required which, to a great extent, is clearly identical to that of a group transmission, but differs from group transmissions, provided with a synchronized range change group. A suitable method for shifting actuation of a group transmission, having an unsynchronized range change group, has been proposed, for example, in DE 101 52 857 A1. In the method, it is essentially provided that, during a range change gear shift, the front-mounted group and the range change group first are shifted to their neutral position to interrupt the energy flow, the main transmission is decelerated by way of a transmission brake, and subsequently the rotational speed of the prime mover begins to be adjusted to the synchronous rotational speed of the target gear. After shifting of the main transmission, the front-mounted group is synchronizedly shifted to its target ratio stage. When the prime mover reaches the synchronous rotational speed, the target ratio stage of the range change group is activated.
It is, of course, disadvantageous in this known method that the existence of a front-mounted group or of a splitter group front-mounted on the main transmission is presupposed and that the shifting sequence can only be used in a range change upshift, similarly the reaching of the synchronous rotational speed by the prime mover to be expected prior to the activation of the target ratio stage of the range change group is delayed.
With this background, the basic function of this invention is to obtain an improved method for shifting actuation of an automated group transmission of the kind mentioned above which, compared to the known method, makes a faster shifting sequence possible and can also be used in group transmissions having no front-mounted group or no splitter group front-mounted on the main transmission.